Heat exchanger

ABSTRACT

Disclosed is a heat exchanger having a plurality of sheet element arrangements, wherein the arrangements contain a plurality of openings, wherein adjacent openings are separated from one another, wherein in operation the openings are flowed through by a first. The openings extend at least sectionally separately from one another within the sheet element arrangement, wherein adjacent sheet element arrangements are each arranged at a spacing from one another so that a second fluid can flow in the intermediate space between two adjacent sheet element arrangements. At least one of the arrangements is interrupted by a cut-out so that the arrangement has at least one first sheet element and one second sheet element, with the second sheet element being so arranged such that the second sheet element can be flowed through by the first fluid subsequent to the first sheet element, with the cut-out containing a flow-directing element.

The invention relates to a heat exchanger for the exchange of heat between a coolant and a gas which can in particular be air.

The use of heat exchange systems is known in a number of applications from the prior art which can practically not be overseen. Heat exchangers are used in refrigeration systems such as in common domestic refrigerators, in air-conditioning plants for buildings or in vehicles of all kinds, above all in motor vehicles, aircraft and ships, as water coolers or oil coolers in internal combustion engines, in mobile or stationary operation, as condensers or evaporators in refrigerant circuits.

A heat exchanger of this type is known, for example, from U.S. Pat. No. 4,876,778. The structure of the heat exchanger is such that cooling water flows within tubes which are arranged between a plurality of sheets and air flows around the sheets. Cooling water and air flow toward one another in a cross-flow. The provided sheets are arranged in parallel to one another and are separated from one another by spacer elements. Such spacer elements can be formed as corrugated sheets, for example.

In the following, a distinction should be made between “laminar heat exchangers”, on the one hand, and “minichannel heat exchangers” or “microchannel heat exchangers”, on the other hand.

The laminar heat exchangers which have been well known for a very long time serve, like all types of heat exchangers, for the transfer of heat between two media, e.g. from a coolant to air or vice versa. The first fluid flowing in the interior of the channels of the heat exchanger is also called a heat carrier in the following. The second fluid flowing around the channels is called a transport fluid in the following. Both the heat carrier and the transport fluid can be present in the liquid or gaseous state. Water, oil, air or a coolant can be named by way of example as the heat carrier or the transport fluid. One of these media is cooled correspondingly by the heat transfer, whereas the other medium is heated.

Generally, the transport fluid, that is e.g., the air, has a considerably smaller heat transfer coefficient than the heat carrier, that is e.g. the coolant or heating medium, which circulates within the channels of the heat exchanger. This is balanced by greatly different heat transfer surfaces for the two media. The medium having the high heat transfer coefficient flows in the channel. Thin metal sheets, e.g. ribs or lamellae, are attached to its outer side so that the outer surface of the channel has a heat transfer surface which is enlarged in comparison with the inner surface of the channel and at which the heat transfer with the transport fluid takes place.

The ratio of outer surface to inner surface of the channel in this respect depends on the lamella geometry, which is in turn determined by the channel diameter, the arrangement of the channels and the spacing of the channels from one another, and on the lamella spacing d′. The lamella spacing d′ is selected differently for different applications. Purely thermodynamically, however, it should be as small as possible, but not so small that the pressure loss on the side of the transport fluid is too large.

An efficient optimum is at approximately 2 mm, which is a typical value for condensers and dry coolers.

The efficiency is in this respect substantially determined by the fact that the heat which is transferred between the lamella surface and the transport fluid has to be transferred to the channel via heat conduction through the lamellae. This heat transfer is the more effective, the higher the conductivity or the thickness of the lamella is, but also the smaller the spacing between the channels is. One speaks of lamella efficiency here. Aluminum is therefore primarily used as the lamella material today which has a high heat conductivity (approx. 220 W/mK) at economic conditions. The spacing of the channels should be as small as possible in this respect. Thermodynamically, a solution would be ideal which has a plurality of channels with small diameters at a small spacing from one another. A substantial cost factor is, however, also the working time for the widening and soldering of the channels. It would increase very disproportionately with such a geometry.

A new class of heat exchangers, so-called minichannel or also microchannel heat exchangers, was therefore already developed some years ago which are manufactured using a completely different process and almost correspond to the ideal of a laminar heat exchanger. They contain minichannels or microchannels with a very small diameter which is in the order of 1 mm. Extruded aluminum sections are preferably used for the manufacture of these minichannels or microchannels.

A heat exchanger block is essentially made up of one or more laminar heat exchangers or from one or more microchannel heat exchangers, with in each case an inlet side of the heat exchanger block being soldered in a pressure tight manner to an outlet element and with an outlet side of the heat exchanger block being soldered in a pressure tight manner to an inlet element. A connection flange is provided in each case in this respect at the outlet element and at the inlet element of the heat exchanger block including one or more heat exchangers so that the heat exchanger block can be flow-connected to an external system, e.g. to a refrigeration machine, such that the heat carrier can be supplied from the outlet element through the heat exchanger to the inlet element in the operating state for the exchange of heat with the transport fluid under a predefinable operating pressure.

The microchannels are arranged in sheet elements. The microchannels extend substantially parallel to one another and are not connected to one another so that the heat carrier, that is the first fluid, is supplied to the sheet element in a microchannels, flows through the sheet element in this microchannel and leaves again in the same microchannel. The transport fluid flows to the microchannels in cross channels. The transport fluid outputs heat to the heat carrier or takes up heat from the heat carrier via the walls of the sheet element. Due to the cross-flow, the ingoing temperature of the transport fluid therefore differs from its outgoing temperature since heat is either taken up or output on the path through the heat exchanger. This causes an inhomogeneous temperature distribution in the microchannels.

In large-area heat exchangers having a heat exchange surface of a plurality of square meters, these temperature differences can result in heat stresses and thus in mechanical stresses of the microchannels which can result in damage to the heat exchanger.

It is therefore an object of the invention to homogenize the temperature distribution in the coolant in the flow direction of the gas.

The object of the invention is satisfied by a heat exchanger having the following features: The heat exchanger has a housing which contains a plurality of sheet element arrangements. The sheet element arrangements contain openings, for example in the form of tubes, which can be flowed through by a first fluid in the operating state. Microchannels in the sense of the preceding statements can also be provided. The openings extend at least sectionally separate from one another within the sheet element arrangement. Adjacent sheet element arrangements are each arranged at a spacing from one another so that a second fluid can flow in the intermediate space between two adjacent sheet element arrangements. The flow direction of the second fluid preferably takes place substantially cross-wise to the flow direction of the first fluid. This means that the first fluid and the second fluid preferably flow in a cross-flow toward one another.

At least one of the sheet element arrangements is interrupted by a cut-out so that the sheet element arrangement has at least one first sheet element and one second sheet element. The second sheet element is arranged with respect to the first sheet element such that the second sheet element can be flowed through by the first fluid subsequent to the first sheet element, with the cut-out containing a flow-deflecting element. A mixture of the individual flows of the first fluid which reach the cut-out via the openings takes place within the cut-out.

In accordance with an embodiment, the cut-out is designed such that a plurality of openings open unto the cut-out at a second end of the first sheet element and the first fluid can in turn be fed from the cut-out into a plurality of openings at a first end of the second sheet element. The cut-out can in particular be designed such that a plurality of tubes, channels or microchannels open into such a cut-out at a first end thereof and the first fluid is in turn fed from the cut-out into a plurality of tubes, channels or microchannels of the second sheet element.

In accordance with an embodiment, the cut-out contains a flow disruption element so that an eddy formation and/or deflection of the flow takes place. Alternatively or additionally to this, the cut-out can contain a static mixer. The cut-out can be surrounded by a jacket element which is connected in a fluid-tight manner to the first and second sheet elements. The jacket element can in particular contain the flow-directing element such as grooves and/or fins and/or projections. The cut-out is formed by the second end of the first sheet element, by the first end of the second sheet element and by the jacket element, with the first sheet element and the second sheet element having a common center plane and the sheet elements being arranged behind one another with respect to the flow direction of the first fluid.

The openings can in particular be formed as channels in the sheet elements. The grooves can be arranged at least sectionally at an angle to the channels. The grooves can include an angle with the channels which is in the range from 10° up to and including 75°, preferably in the range from 10° up to and including 60°, particularly preferably in the range from 10° up to and including 45°.

In accordance with an alternative embodiment, the jacket element can include projections which project into the cut-out and form flow disruption elements.

The cut-out advantageously extends over between 5% and 40% of the length of the heat exchanger, with the length of the heat exchanger being measured in the main flow direction of the first fluid flowing within the sheet elements. To ensure a temperature compensation over the total width of the heat exchanger, it is advantageous if the cut-out extends substantially over the total width of the heat exchanger.

In accordance with an embodiment, an installation element can be provided for maintaining the distance between two adjacent sheet elements. The installation element can in particular be formed as a corrugated, thin-walled spacer element.

The invention also relates to a method of operating a heat exchanger in accordance with any one of the preceding embodiments including a step in which the first fluid is mixed on its flow path within the sheet element arrangement between its inlet into the sheet element arrangement and its outlet from the sheet element arrangement. In accordance with an advantageous variant, the second fluid flows between adjacent sheet element arrangements in a cross-flow to the first fluid. The second fluid thus flows transversely to the first fluid. The first fluid can in particular be a coolant. The second fluid can in particular be a gas, advantageously air. The sheet elements can be made as sections in which the coolant moves in a plurality of separate, parallel channels. Viewed in the direction of the first fluid, these channels for the first fluid are disposed after one another.

The heat transfer differs from one channel to the next channel for a plurality of reasons. On the one hand, the floating temperature difference varies due to different local temperatures of the first fluid; on the other hand, the ratio of liquid phase to gaseous phase can vary when the second fluid is present in a liquid phase and in a gaseous phase, which influences the total efficiency of the heat exchanger.

More than one cut-out can in particular be arranged in a sheet element arrangement. When a plurality of cut-outs are provided, each of the cut-outs can contain a flow-deflecting element. In particular a mixture of the second fluid can take place so that a temperature balance occurs in the second fluid and a homogenization of the temperature profile occurs over the length and the width of the heat exchanger.

The performance of a heat exchanger can in particular be substantially increased when the sheet element arrangements have a large width and/or length and/or the flow speed of the first fluid is small.

A heat exchanger in accordance with the invention can in particular be built in a larger length and the number of the sheet arrangements can be reduced by up to two thirds with respect to the prior art.

The invention will be explained in the following with reference to the drawings. There are shown:

FIG. 1 a view of a sheet element arrangement in accordance with a first embodiment of the invention;

FIG. 2 a view of a stack of sheet element arrangements;

FIG. 3 a side view of an arrangement of sheet elements;

FIG. 4 a plan view of the arrangement of sheet elements in accordance with FIG. 3;

FIG. 5 a detail of the plan view in accordance with FIG. 4;

FIG. 6 a side view of an arrangement of sheet elements in accordance with a second embodiment;

FIG. 7 a plan view of the arrangement of sheet elements in accordance with FIG. 6;

FIG. 8 a detail of the side view in accordance with FIG. 6;

FIG. 9 a view of a stack of sheet elements; and

FIG. 10 a view of a sheet element arrangement in accordance with the second embodiment of the invention.

FIG. 1 illustrates a view of a sheet element arrangement 2 in accordance with a first embodiment of the invention for a heat exchanger 1. The sheet element arrangement includes a first sheet element 3, a second sheet element 4 and a cut-out 5 which is arranged between the first sheet element 3 and the second sheet element 4. A first fluid 7 enters unto the first sheet element 3, flows through the openings 6 in the direction of the cut-out 5, into the cut-out 5, and subsequently leaves the cut-out 5 through the openings 6 of the second sheet element 4.

The first fluid 7 is a heat carrier and can be either a heating medium or a cooling medium. The first fluid 7 is preferably present in the liquid aggregate state since its heat conductivity is substantially higher than that of a gaseous fluid and the heat exchange area available for the first fluid is smaller than for the second fluid. The openings 6 in the first and second sheet elements 3, 4 have a spacing from one another so that each of the openings 6 forms a channel 9 separate from the other openings and closed at the jacket side. The channel 9 can in particular have the form of a tube and/or can be formed as a microchannel having the dimensions described in the introduction.

The first fluid 7 flows through these microchannels which can have corrugated installations which are not shown in the drawing. These corrugated installations serve for the enlarging of the heat exchange surface available for the heat transfer. Lattice structures, mesh-like structures or porous structures can naturally also be provided instead of the corrugated installations. The channels 9 can be formed as tubes or also as oval or quadrangular, in particular rectangular, channels which have been manufactured from an extruded section by means of an extrusion process. A plurality of microchannels can hereby be arranged in the sheet element arrangement. In particular aluminum or an aluminum alloy has proven itself as a material for the channels 9.

The first sheet element 3 has a first end 16 which contains the inlet openings of the openings 6 through which the first fluid 7 is conducted into the first sheet element 3. The outlet openings of the openings 6 are arranged at a second end 17 of the first sheet element 3.

The second sheet element 4 has a first end 18 which contains the inlet openings of the openings 6 through which the first fluid 7 is conducted into the second sheet element 4. The outlet openings of the openings 6 are arranged at a second end 19 of the second sheet element 4.

In particular in accordance with FIG. 1, the cut-out 5 is designed so that a plurality of openings 6 at the second end 17 of the first sheet element 3 open into the cut-out 5 and the first fluid 7 can in turn be fed from the cut-out 5 into a plurality of openings which are arranged at the first end 18 of the second sheet element 4.

The cut-out is a hollow space which extends between the first and second sheet elements 3, 4 and which is surrounded by a jacket element. The cut-out 5 is formed by the second end 17 of the first sheet element 3, by the first end 18 of the second sheet element 19 and by the jacket element, with the first sheet element 3 and the second sheet element 4 having a common center plane and the sheet elements 3, 4 being arranged behind one another with respect to the flow direction of the first fluid 7.

In the present representation, the jacket element is made up of an upper jacket part 10 and a lower jacket part 11. The upper jacket part 10 is shown in the non-assembled state in the manner of an exploded drawing so that the structure of the lower jacket part 11 is visible. Instead of an upper and lower jacket part, the jacket element can also be made in one piece. The first and second sheet elements can be subsequently connected to the jacket element, that is, they can, for example, be plugged into openings of the jacket element for the first and second sheet elements. A fluid-tight connection between the sheet element is made possible by a seal element, by a slight oversize of the sheet element relative to the jacket element or by subsequent welding of the jacket element and the sheet element.

The upper jacket part 10 and the lower jacket part 11 have flow-directing elements 20. The flow-directing elements 20 are formed as fins 21. Alternatively to this, only one of the upper or lower jackets parts can naturally have fins 21 and the respective other one of the upper or lower jacket parts can have a smooth surface or grooves 23. A plurality of current-directing elements 20 is usually provided, in particular when the heat exchanger has a large width. However, a single flow-directing element would satisfy the function of a deflection of the flow of the first fluid 7.

The flow-directing element 20 can in particular be arranged at least sectionally at an angle to the channels 9. The flow-directing element preferably includes an angle with the channels which is in the range from 10° up to and including 75°, preferably in the range from 10° up to and including 60°, particularly preferably in the range from 10° up to and including 45°.

To achieve an improved mixing, the flow-directing elements 20 of the upper jacket part 10 can include a different angle 27 with the channels 9 than the current-directing elements 20 of the lower jacket part 11. The angle 27 is shown in FIG. 5.

In accordance with an alternative embodiment, the jacket element, or at least one of the upper or lower jacket parts 10, 11, contains projections 25 which project into the cut-out 5 and form flow disruption elements.

The cut-out 5 advantageously extends over between 5% and 40% of the length 26 of the heat exchanger, with the length 26 of the heat exchanger being measured in the main flow direction of the first fluid 7 flowing within the sheet elements 3, 4. In FIG. 3, the length 26 of the heat exchanger is shown as the sum of the lengths of the sheet elements and of the cut-out 5.

The cut-out 5 can in particular extend substantially over the total width 28 of the heat exchanger 1. The width 28 of the heat exchanger 1 substantially corresponds to the width of the sheet element arrangement and is shown in FIG. 5.

FIG. 2 shows a stack of sheet element arrangements 2, 12, 22 which form a heat exchanger 1. These sheet element arrangements 2, 12, 22 are located in a housing which is omitted in the representation to be able to better illustrate the operation of the heat exchanger. Each of the sheet element arrangements 2, 12, 22 can be made up of the first and second sheet elements 3, 4 shown in FIG. 1 as well as of a cut-out 5.

A second fluid 8, also called a transport fluid, can flow above and/or beneath each sheet element arrangement 2, 12, 22. The second fluid 8, which is usually gaseous, can be heated by means of the heating medium or can be cooled by means of the coolant depending on the desired function of the heat exchanger 1.

The intermediate space 15, which is flowed through by the second fluid 8, can contain installation elements 13 which are shown as corrugated structures in FIG. 2. The installation elements 13 are in heat conductive contact with the respective adjacent sheet element arrangements so that heat can be transferred via the installation elements 13. The installation elements 13 thus also serve for the increase of the heat exchange surface. The installation elements can also be formed as fins or, as above, contain lattice structures, mesh-like structures or porous structures. Furthermore, the installation elements can also be formed as serrated sections in V-shape or W-shape.

FIG. 3 shows a side view of a sheet element arrangement in accordance with the first embodiment. The thickness of the jacket element, composed of an upper and lower jacket part 10, 11, in this respect exceeds the thickness of the first and second sheet elements 3, 4. This has the consequence that the spacing between adjacent sheet element arrangements is smaller at the point at which the jacket element is located. In accordance with the variant shown in FIG. 10, installation elements 29 are therefore provided between the jacket elements of adjacent sheet element arrangements which have a smaller height than the installation elements 13.

FIG. 4 shows a plan view of the arrangement of sheet elements in accordance with FIG. 3. The view corresponds to the arrangement of FIG. 1 when the upper jacket part 10 is removed. The length of the sheet element arrangement 2 is here defined as the length of the first and second sheet elements 3, 4 as well as the length of the cut-out 5 which is not visible here.

FIG. 5 is a detail of the plan view in accordance with FIG. 4 and shows a part of the lower jacket element 11 as well as the fins 21 which form the flow-directing element 20. The width 28 of the sheet element arrangement is likewise shown.

FIG. 6 shows a side view of a sheet element arrangement in accordance with a second embodiment of the invention. This sheet element arrangement differs by the structure of the first and second sheet elements 3, 4 which have a porous structure through which the first fluid 7 can flow instead of channels. The cut-out contains a plurality of projections 25 as flow-directing elements which can form disruption elements 24 for the flow. These projections can be local elevated portions or can also be fins or grooves extending over a part of the length and/or width of the cut-out.

FIG. 7 shows a plan view of the arrangement of sheet elements in accordance with FIG. 6 and has an analog structure to FIG. 3; see therefore the description of FIG. 3.

FIG. 8 shows a detail of the side view in accordance with FIG. 6. The flow-directing elements 20 are formed as fins. The fins of the upper jacket part and of the lower jacket part come to lie on one another in the installed state. The first fluid can thus only flow past these fins and is deflected by the fins and mixed by the deflection and/or eddying. The temperature drop which the first fluid has in the direction of the width of the heat exchanger is thus balanced.

FIG. 9 shows a view of a stack of sheet elements similar to FIG. 2. Unlike FIG. 2, the installation elements 29 between the jacket elements of the cut-outs 5 are also shown which differ in their height from the installation elements 13 which are arranged between the sheet elements 3, 4.

FIG. 10 shows a view of a sheet element arrangement in accordance with the second embodiment of the invention. The upper and lower jacket parts 10, 11 are shown as transparent elements so that the projections are visible which extend cross-wise over a part of the inner surface of at least one of the jacket parts in the form of fin pairs. 

1. A heat exchanger (1) which has a housing which contains a plurality of sheet element arrangements (2, 12, 22), wherein the sheet element arrangements contain a plurality of openings (6), wherein adjacent openings are separated from one another, wherein the openings are flowed through by a first fluid (7) in the operating state, wherein the openings extend at least sectionally separately from one another within the sheet element arrangement, wherein adjacent sheet element arrangements are each arranged at a spacing from one another so that a second fluid (8) can flow in the intermediate space (15) between two adjacent sheet element arrangements (2, 12, 22), wherein at least one of the sheet element arrangements (2, 12, 22) is interrupted by a cut-out (5) so that the sheet element arrangement has at least one first sheet element (3) and one second sheet element (4), with the second sheet element (4) being arranged with respect to the first sheet element (3) such that the second sheet element (4) can be flowed through by the first fluid (7) subsequent to the first sheet element (3), with the cut-out (5) containing a flow-directing element (20).
 2. The heat exchanger in accordance with claim 1, wherein the cut-out (5) is designed so that a plurality of openings (6) at a second end (17) of the first sheet element (3) open into the cut-out (5) and the first fluid (7) can in turn be fed from the cut-out (5) into a plurality of openings (6) which are arranged at a first end (18) of the second sheet element (4).
 3. The heat exchanger in accordance with claim 1, wherein the cut-out contains a flow disruption element and/or a static mixer.
 4. The heat exchanger in accordance with claim 1, wherein the cut-out is surrounded by a jacket element which is connected in a fluid-tight manner to the first and second sheet elements.
 5. The heat exchanger in accordance with claim 4, wherein the jacket element contains the flow-directing element (20) which can be designed as a fin (21) and/or as a groove (23) and/or as a projection (25).
 6. The heat exchanger in accordance with claim 1, wherein the cut-out (5) is formed by the second end (17) of the first sheet element (3), by the first end (18) of the second sheet element (4) and by the jacket element (10, 11), with the first sheet element (3) and the second sheet element (4) having a common center plane and the sheet elements being arranged behind one another with respect to the flow direction of the first fluid (7).
 7. The heat exchanger in accordance with claim 1, wherein the openings (6) are formed as channels (9) in the sheet elements (3, 4).
 8. The heat exchanger in accordance with claim 7, wherein the flow-directing element (20) is arranged at least sectionally at an angle (27) to the channels (9).
 9. The heat exchanger in accordance with claim 7, wherein the flow-directing element (20) includes an angle (27) with the channels (9) which is in the range from 10° up to and including 75°, preferably in the range from 10° up to and including 60°, particularly preferably in the range from 10° up to and including 45°.
 10. The heat exchanger in accordance with claim 4, wherein the jacket element contains projections which project into the cut-out and form flow disruption elements.
 11. The heat exchanger in accordance with claim 1, wherein the cut-out extends over between 5% and 40% of the length (26) of the heat exchanger, with the length (26) of the heat exchanger being measured in the main flow direction of the first fluid (7) flowing within the sheet elements.
 12. The heat exchanger in accordance with claim 1, wherein the cut-out (5) substantially extends over the total width (28) of the heat exchanger.
 13. The heat exchanger in accordance with claim 1, wherein an installation element (13) is provided for maintaining the spacing between two adjacent sheet element arrangements (2, 12, 22).
 14. The method of operating a heat exchanger in accordance with claim 1, including a step in which the first fluid (7) is mixed on its flow path within the sheet element arrangement (2, 12, 22) between its inlet into the sheet element arrangement and its outlet from the sheet element arrangement.
 15. The method in accordance with claim 14, wherein the second fluid (8) flowing between adjacent sheet element arrangements flows in a cross-flow to the first fluid (7). 